a) Field of the Invention
The present invention relates to a radiation detector used in a radiologic diagnostic apparatus such as a positron emission tomography apparatus (e.g., positron computer tomography; positron CT).
b) Background art
A detector has been used which comprises a photomultiplier tube and a scintillator divided into a plurality of scintillator chips and connected to an entrance window of the photomultiplier tube, as such a radiation detector for the positron emission tomography apparatus. The .gamma.-rays emitted from a radiation source in a subject to be examined are, in order, made incident upon the scintillator chips of the radiation detector to thus emit scintillation light rays. The scintillation light rays are received by the photomultiplier tube and photoelectrically converted into electrical signals by the action of the tube which correspondingly outputs the successive electrical signals. More specifically, detectors have been used comprising a scintillator 2 joined to the entrance window 1a of four photomultiplier tubes 11, 12, 13 and 14, the scintillator 2 having grooves, whose depth at the peripheral portion is greater than that of the grooves present at the central portion and which are divided in the scintillator 2 into a plurality of scintillator chips 21, 22, ..., as shown in FIG. 5. When .gamma.-rays are made incident upon the radiation detector or the scintillator 2, they are, in order, received by different scintillator chips 21, 22, ..., with the lapse of time since the radiation detector is rotated by a driving means. As a result, each scintillator chip 21, 22, ... emits scintillation light rays upon being irradiated with the .gamma.-rays. Since the plurality of scintillator chips 21, 22, ... are separated by the grooves formed so that those present at the peripheral portion have a depth deeper than that of those present at the central portion. The scintillation light rays emitted when the scintillator chip 21 is, for instance, irradiated with the incident .gamma.-rays are principally received by the photomultiplier tube 13, while those emitted when the scintillator chip 22 is irradiated with the incident .gamma.-rays are received by the photomultiplier tube 13 and 14. Thus, the radiation detector can process the intensities of light detected by the photomultiplier tubes 11 to 14 and can accordingly specify a scintillator chip which emits light. The finer the divided scintillator chips 21, 22, ..., the higher the space resolution of the radiation detector and the clearer the tomographic image obtained by the positron emission tomography apparatus provided with the radiation detector.